Oil canning is one of the most common (and frustrating) issues in trailer manufacturing. If you’ve ever noticed wavy or distorted panels on a cargo or enclosed trailer, you’ve seen oil canning in action. For engineers, OEMs, and trailer manufacturers, understanding what causes oil canning, how it impacts performance, and how to prevent it is critical when selecting the right trailer siding material.

In this article, we’ll break down what oil canning is, why it happens to trailers with aluminum and cheap composite panels, how it affects trailer performance and appearance, and how PolyCor™ AP composite trailer siding eliminates this issue.

What Causes Oil Canning?

Oil canning refers to the visible waviness or distortion that appears in flat metal or composite panels, especially large surfaces like trailer siding. The term comes from the way the panel flexes in and out, similar to pressing on the bottom of an old oil can. It is most commonly associated with trailers that use aluminum panels, thin-gauge metal panels, or cheap knock-off composite panels.

The oil canning issue is primarily caused by thermal expansion and contraction. As panels repeatedly expand and contract over time, they lose their flatness and develop permanent waviness. Common factors that drive this change include:

• Temperature fluctuations: Trailers experience extreme heat and cold, from hot highways to freezing storage conditions.

• Material movement: Aluminum expands when heated and contracts when cooled, leading to stress across large panels.

• Panel size and thickness: Larger, thinner panels are more prone to visible distortion.

• Improper installation or fastening: Uneven tension or spacing can amplify the effect.

• Low-quality materials: Cheap composite panels often lack the structural integrity to resist movement.

Why Is Oil Canning a Problem for Trailers?

Oil canning isn’t just a cosmetic issue; it can impact performance, branding, and long-term durability. Visible waviness can detract from a clean, professional appearance, which is especially important for trailers used for branding or customer-facing applications. From a performance standpoint, repeated panel movement can place stress on fasteners, seams, and joints, potentially leading to premature wear or maintenance issues. Over time, this constant expansion and contraction can also contribute to material fatigue, reducing the overall lifespan of the panel and affecting the structural integrity of the trailer exterior.

Why Is Aluminum Trailer Siding Is Prone to Oil Canning

Aluminum has long been a go-to material for trailer siding due to its lightweight properties, but it comes with tradeoffs. Common challenges with aluminum panels include:

• High thermal expansion: Aluminum expands and contracts significantly with temperature changes.

• Visible surface distortion: Even minor movement becomes noticeable across large, flat panels.

• Weight considerations: Standard 0.050" aluminum is approximately 25% heavier than PolyCor AP.

• Long-term performance concerns: Repeated movement can lead to surface inconsistencies, reduced aesthetic quality, and increased maintenance.

Because of these limitations, many OEMs and trailer manufacturers are actively searching for alternatives to aluminum trailer siding.

Are All Composite Trailer Panels Better Than Aluminum?

Not necessarily. As demand for composite trailer siding panels grows, lower-cost alternatives have entered the market. While they may appear similar to premium materials like PolyCor AP, they often lack the engineering required to perform in demanding environments. As a result, these materials may still experience oil canning or similar distortions, especially over time.

In addition to surface waviness, cheap composite panels can introduce serious long-term performance risks. Lower-quality materials often lack proper core construction and bonding, which can lead to delamination, reduced impact resistance, and poor performance in extreme temperatures. Over time, this can result in increased maintenance, premature panel failure, and higher total cost of ownership. For trailer manufacturers, these issues don’t just affect durability; they can impact customer satisfaction, brand reputation, and warranty claims.

It’s also important to be aware of misleading claims in the market. Some distributors or manufacturers may advertise “PolyCor” or “PolyCore” trailer panels, but PolyCor™ AP is exclusively available through Piedmont Plastics. These imitation products are not engineered to the same standards and often lack the proven performance, quality control, and traceability that come with genuine PolyCor AP. To ensure you’re getting the real material, always verify your source and confirm that your panels are supplied directly by Piedmont Plastics.

How PolyCor AP Resists Oil Canning and Enhances Trailer Performance

Piedmont Plastics developed PolyCor AP to directly address the performance limitations of aluminum. Engineered for superior dimensional stability, weatherability, and harsh road conditions, PolyCor AP maintains its sleek look wile aluminum crumples. For trailer manufacturers, this means delivering a cleaner, more professional finish across large panels, an essential advantage for cargo trailers, enclosed trailers, and specialty vehicle applications where visual quality matters.

Key Benefits of PolyCor AP

1. Oil canning resistance
PolyCor AP prevents the waviness and distortion common in aluminum and low quality composite panels.

• Prevents visible waves and distortion

• Maintains a smooth, flat exterior surface

• Supports consistent appearance across large panels

2. Lightweight performance
PolyCor AP delivers a lightweight solution without sacrificing strength.

• Lighter than traditional aluminum

• Easier to handle and install

• Helps improve towing efficiency and payload capacity

3. Durable paint system
PolyCor AP features a high performance coating built for long lasting durability.

• Long term durability in outdoor conditions

• Strong resistance to weather and UV exposure

• Easy to clean and maintain

4. Consistent long term performance
PolyCor AP delivers reliable performance over the life of the trailer.

• Reduces long term maintenance issues

• Helps extend trailer lifespan

• Delivers consistent performance across builds

Why Manufacturers Are Switching to Composite Trailer Siding

The shift from aluminum to advanced composites like PolyCor AP is driven by a need for improved surface quality, reduced maintenance, better performance in varying climates, and enhanced branding capabilities. For OEMs, the goal is simple: deliver a product that looks better, lasts longer, and performs reliably.

Choosing the Right Trailer Siding Material

Working with an experienced supplier ensures you select a material that meets both performance and cost expectations. When evaluating options, purchasers should consider:

• Resistance to oil canning

• Thermal stability

• Weight

• Surface quality

• Long-term durability

• Ease of installation

Work with Piedmont Plastics

Piedmont Plastics is the exclusive distributor of the PolyCor product line, providing trailer manufacturers with proven material solutions for oil canning and the trailer industry. If you’re looking to eliminate oil canning and improve the quality of your trailer builds, PolyCor AP offers a reliable, engineered solution.

With local inventory, technical expertise, and a network of branches across North America, Piedmont Plastics helps OEMs and fabricators find the right materials for their applications. Get in touch with our sales team today for more information!